In recent years, in order to achieve optical transmission at a low loss and a high density, various on-chip optical interconnects have been proposed in which data input and output are performed at a high speed and with a low power consumption. In order to achieve such an optical interconnect, attention is paid to a microring laser diode (LD) using a microring resonator, which is applied as a small light source. In this type of microring LD, the key to put it into practice is stabilization of circulating modes.
In order that stabilization of the circulating modes be improved, it has been proposed that in a microring LD, a light-emitting portion formed of a group III-V compound semiconductor and a feedback waveguide formed of a group III-V compound semiconductor are provided. However, in this structure, an absorption loss in the waveguide is great. Furthermore, the radius of curvature of the feedback waveguide cannot be greatly reduced. Thus, it is hard to make a microring resonator smaller.